...(Acamptopappus shockleyi), white bursage (Ambrosia dumosa), shadscale (Atriplex confertifolia), Nevada ephedra (Ephedra nevadensis), winterfat (Krascheninnikovia lanata), range ratany (Krameria erecta), and creosote bush (Larrea tridentata). The initiation of leafing, flowering, and fruiting phenologies was significantly delayed, and flowering success was significantly reduced in all shrub species occurring within and around the nest area compared to the adjacent non-nest area. The interval between initial dates of each major phenophase (leafing, flowering, and fruiting) of all shrub species became larger in nest relative to non-nest areas. The infestation of seed-harvester ants had a detrimental effect on the phenological events of seven Mojave Desert shrub species in southern Nevada.

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The seed-harvester ant (Pogonomyrmex rugosus) occurs in arid and semiarid plant communities throughout much of southwestern United States (Carlson and Whitford 1991). Nests of harvester ant species are generally clear of plants at least in the central area surrounding the single nest entrance where ant activities are most intense (Beattie and Culver 1977; Lei 1999). Previous studies have found changes in plant diversity and composition (Beattie and Culver 1977; Lei 1999), population densities (Hobbs 1985; Lei 1999), and vegetation production (Rogers and Lavigne 1974) associated with ant nests.

Studies of plant phenology are crucial to understand the resource base of populations, communities, and ecosystems. Phenological events of selected Mojave Desert shrub species were studied in Rock Valley of southern Nevada (Wallace and Romney 1972; Ackerman and Bamberg 1974; Beatley 1974; Rundel and Gibson 1996). Yet, ecological impacts of seed-harvester ants on the phenological attributes of the surrounding shrub species have not been documented in Las Vegas Valley. Rock and Las Vegas Valleys are similar in climatic conditions, species composition, vegetation cover, community structure, soils, geology, and topography. The objective of this study was to quantify leafing, flowering, and fruiting phenologies of all seven Mojave Desert species--Shockley's goldenhead (Acamptopappus shockleyi), white bursage (Ambrosia dumosa), shadscale (Atriplex confertifolia), Nevada ephedra (Ephedra nevadensis), winterfat (Krascheninnikovia lanata), range ratany (Krameria erecta), and creosote bush (Larrea tri-dentata), occurring in the nest area compared to the adjacent non-nest area in Las Vegas Valley.

Methods

Study Site

The field study was conducted in the southwestern part of Las Vegas Valley in southern Nevada (36[degrees]04'N; 115[degrees]10'W). The climate is arid with hot, dry summer and cool, episodic wet winters. The mean monthly air temperature and precipitation for the years 2000 through 2003 are shown in Table 1 (NOAA, Las Vegas). The mean length of the frost-free period...

NOTE: All illustrations and photos have been removed from this article.



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